On our cruise in April on the Caribbean Princess the chef went all out on formal nights.
The most memorable meals of the cruise!

There is such a range of attire that you will not feel out of place. But you will feel like a millionaire for the night! You have paid for all this luxury - enjoy it!

A woman could wear a simple black skirt and shell top with an inexpensive pair of sparkly earrings for effect if you wish. Your husband will be fine with his sport jacket. Don't worry that everyone else will look like they are attending the Academy Awards. They won't.